The nuclear transfer (NT) technique in the mouse has enabled us to generate cloned mice and to establish NT embryonic stem (ntES) cells. Direct nuclear injection into mouse oocytes with a piezo impact drive unit can aid in the bypass of several steps of the original cell fusion procedure. It is important to note that only the NT approach can reveal dynamic and global modifications in the epigenome without using genetic modification as well as generating live animals from single cells. Thus, these techniques could also be applied to the preservation of genetic material from any mouse strain instead of preserving embryos or gametes. Moreover, with this technique, we can use not only living cells but also the nuclei of dead cells from frozen mouse carcasses for NT. This chapter describes our most recent protocols of NT into the mouse oocyte for cloning mice and for the establishment of ntES cells from cloned embryos.